This paper shows the improvements in imaging performance on the ASML PAS5500/800TM, the PAS5500/850BTM and the TWINSCANTM AT:850BTM Step & Scan systems. During setup, the lens aberrations are measured by the TAMIS technique and optimized. This gives excellent imaging performance for aberration sensitive features such as 'two bar,' the DRAM isolation pattern and isolated lines printed with alternating PSM. Lithographic tests based on these features were developed and tested on a number of 800 and 850 systems and gave results well within specification limits. Consequently, the imaging performance has been improved for a wide range of applications.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.